A New Jersey landscaper found the first signs of the destructive emerald ash borer last week. He was checking the health of ash trees at a strip shopping center in Bridgewater, Somerset County, when he spotted the telltale damage. He alerted state officials, who shared specimens with a federal lab, which confirmed everyone’s suspicions: The emerald ash borer had come to New Jersey.

An invasive beetle that has killed tens of millions of ash trees across the country, the insect had already been detected in nearby Pennsylvania and New York counties. Until showing up in Bridgewater, though, it hadn’t been seen in New Jersey, where some experts say it’s now likely to take up residence.

“It’s going to spread” into South Jersey, said certified forester Bob Williams, owner and founder of Pine Creek Forestry in Laurel Springs, Camden County. “We have ash forests down here, so it’s coming. “It would be a mistake to act like it’s not,” he said. “I think it’s a serious problem.”

Using a computer model to direct them, state officials are checking trees in Camden, Burlington, Gloucester, Salem, Mercer, and Monmouth and in counties north to determine the degree of infestation, officials said.

The New Jersey Department of Agriculture, state Department of Environmental Protection’s Forestry Service, and U.S. Department of Agriculture’s Animal and Plant Health Inspection Service have set out more than 300 traps in those areas. This is the fourth year traps have been set out, but amid heightened concerns. The beetle will be active for the next month or two.